# RE: OMEGA BLOCK with mixture model?

From: Mark Sale - Next Level Solutions <mark>
Date: Tue, 14 Apr 2009 08:46:23 -0700
 Nele, You'll need to rearrange/reassign your ET= As so that you can have correlation between CL(1) and F1, and CL(2) and F1,= but not CL(1) and CL(2).  So, put ETA(1) on CL(1), ETA(2) on F1 and E= TA(3) on CL(2), then \$OMEGA like this:\$OMEGA BLOCK(3) 0.1=             &n= bsp;       ;CL(1) 0.01 0.1       &nbs= p;     ;F10 =      0.01   0.1  ;CL(2)This is= the BAND matrix, which is permitted.Mark Sale MD Next Level Solutions, LLC www.NextLevelSolns.com 919-846-9185 -------- Original Message -------- Subject: [NMusers] OMEGA BLOCK with mixture model? From: nele.plock Date: Tue, April 14, 2009 11:08 am To: nmusers Dear all, I am trying to fit a PK model to oral data. I= n the data, we observed two things: First, CL seems to be negatively correl= ated with F1. Secondly, there seem to be two subpopulations in the exposure= , let's say a large group with 'normal' and a second group with high exposu= re. I would like to identify the subpopulations using a mixture model, but = keep the correlation between CL and F1. Now I ran into problems when coding= the \$OMEGA BLOCK. I f= igured the block to be something like: \$OMEGA BLOCK(3) 0.1  ;CL1 0 FIX 0.1 ;= CL2 0.01 0.01 0.1 ;F1 The error message that appe= ars is: a covariance is zer= o, but the block is not a band matrix I assume that this means that I am not allowed to fix the c= orrelation between the two clearance-omegas to zero. However, it would be u= nreasonable to allow a correlation, because the omegas belong to different = subpopulations, so there can't be a correlation. On the other hand, I did n= ot include subpopulations for F1, so how can I keep this correlation to bot= h CL-subgroups? Any th= oughts on this would be highly appreciated! Best wishes Nele ____________________= __________________________________________ Dr. Nele Plock Phar= macometrics -- Modeling and Simulation Nycomed GmbH Byk-Gulden= -Str. 2 D-78467 Konstanz, Germany Fon: (+49) 7531 / 84 -  = ;4759 Fax: (+49) 7531 / 84 - 94759 mailto: nele.plock com http://www.nycomed.com County Court: Fre= iburg, Commercial Register HRB 701257 Chairman Supervisory Board: Charl= es Depasse Management Board: Dr. Barthold Piening, Gilbert Rademacher, = Dr. Anders Ullman ``` ---------------------------------------------------------------------- Proprietary or confidential information belonging to Nycomed Group may be contained in this message. If you are not the addressee indicated in this message, please do not copy or deliver this message to anyone. In such case, please destroy this message and notify the sender by reply e-mail. Please advise the sender immediately if you or your employer do not consent to Internet e-mail for messages of this kind. Opinions, conclusions and other information in this message that pertain to the sender's employer and its products and services represent the opinion of the sender and do not necessarily represent or reflect the views and opinions of the employer. ---------------------------------------------------------------------- ```